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New Observations on Rhabdopleura Kozlowskii (Pterobranchia) from the Bathonian of Poland

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New Observations on Rhabdopleura Kozlowskii (Pterobranchia) from the Bathonian of Poland ACT A PAL A EON T 0 LOG IC A POLONICA Vol. XVI 1971 No. ( CYPRIAN KULICKI NEW OBSERVATIONS ON RHABDOPLEURA KOZLOWSKII (PTEROBRANCHIA) FROM THE BATHONIAN OF POLAND Abstract. - Specimens of Rh. kozlowskii Kulicki, 1969 have here been described from the Bathonian of southern Poland. A secondary layer, never observed before, has been found inside zooidal tubes. INTRODUCTION At present, the genus Rhabdopleura is represented by at least two species clearly different from each other, Le. Rh. normani Allman, 1869 and Rh. striata Schepotieff, 1909. All other Recent species display a con­ siderable similarity to Rh. normani and the necessity to distinguish them is called in question by many investigators (Schepotieff, 1906; Dawydoff 1948; Thomas & .Davis, 1949; Burdon-Jones, 1954 and others). The species Rh. compacta Hincks, 1880 has recently been restored by Stebbing (1970), who concludes that Rh. compacta differs from Rh. normani mostly in the form of colonies and lack of ring-shaped part of the stolon. The following three fossil species have hitherto been described: Rh. vistulae Kozlowski, 1956 from the Danian of Poland, Rh. eocenica Tho­ mas & Davis, 1949 from the Eocene of England, and Rh. kozlowskii Kulicki, 1969 from the Callovian of Poland. The specimens of Rh. kozlowskii, described in the present paper, were etched with hydrochloric acid fTom ca1careous-marlyconcretions which occur in black and dark-gray Bathonian clays, Morrisiceras morrisi Zone (R6zycki, 1953) of Blanowice near Zawiercie. The concretions, varying in shape, are mostly spherical or ellipsoidal and fluctuate in size between a few and some scores of centimetres. Many of the concretions collected contain a macrofauna of molluscs or pieces of wood. The remains of hydroids, scolecodonts, organic linings of foraminifers, plant remains and other, unidentified remains, including many similar to the Callovian ones 416 CYPRIAN KULICKI from Luk6w (Kulicki, 1969), were etched out along with the remains of Rhabdopleura. The specimens of Rh. kozlowskii from the Bathonian of Blanowice are preserved much the same as those fram the Callovian of I:.uk6w and are represented by these same elements of tubarium. Specim€ns of Rh. normani from Bergen, Norway, have been used by the present writer as a comparative material. The terminology of the elements of tubarium has been adopted according to Kozlowski (1956) and the writer's previous work (Kulicki, 1969). Schepotieff's definition "st€ril Knospe" (sterile bud) was replaced by the writer (after Stebbing) with the term "dormant bud". Schepotieff (1907) believed that the buds contained in cysts, could not be turned into zooids. Stebbing studies (1970) have, however, shown that such buds may develop into normal individuals and, therefore, the term a dormant bud is more appropriate for them. A diagram of fundamental measurements of various elements of tubarium is shown in Fig. 1. A m B Fig. 1. - Diagram of fundamental measurements of zooidal (A) and stolonal (B) tubes of the genus Rhabdopleura: 1 inner diameter, 2 outer diameter without fusellar collars, 3 outer diameter with fusellar collar, 4 width of fusellar collar 5 thicknes·s of wall of zooidal tube, 6, 7 width of fusellus, 8 outer diameter of stolonal tube, m marginal membrane. The specimens of Rh. kozlowskii and Rh. normani described in the present paper are housed at the Palaeozoological Institute, Polish Academy of Sciences, for which the abbreviation Z. Pal. is used. RHABDOPLEURA KOZLOWSKII FROM THE BATHONIAN 417 DESCRIPTION Family Rhabdopleuridae Harmer, 1905 Genus Rhabdopleura Allman, 1869 Rhabdopleura kozlowskii Kulicki, 1969 (Text-figs. 2-7) 1969. RhabdopLeura kozLowskii Kulicki, 1969; C. Kulicki, The discovery..., pp. 540, 542, 544, 545; Figs. IE, 3B, 4A, 5J. Material. - Thirty-one fragmentary zooidal tubes, seven fragmentary stolonal tubes, 23 variously-sized fragments of stolons and 69 cysts of dormant buds, some of them with stolons. Description. - Zooidal tubes. A diameter of the erect parts of zooidal tubes, the width of fusellar collars not taken into account, varies within limits of 124 and 189 fl, averaging 154 1ft, whereas a diameter of tubes including fusellar collars amounts to 143-235 fl, averaging 178 f-l; a mean width of a fusellar collar amounts to 12 fl. The width of fuselli varies from 20 to 53 !-l, averaging 42/l. Within the range of particular zooidal tubes, the width of fuselli is considerably variable although the differences do not exceed extreme values. In many specimens from Blanowice and Luk6w, one or two layers of skeletal substance, similar to that which forms the fuseliar part of tube and which is termed by the writer a secondary layer (Figs. 3, 7) occur inside zooidal tubes under the fuselar layer. The secondary layer does not display any traces of fusella'r structure. All injuries and cracks of the secondary layer (d. Fig. 3) run along the longitudinal axis of tube. A peculiar texture of secondary layer with parallel and closely spaced, dark striae running along the longitudinal axis of tube are visible in strong magnification. No such texture can, on the other hand, be observed in the fusellar layer. The secondary layer IS frequently thicker inside tubes with small than normal and large diameters. In one case, the secondary layer is double (Fig. 3) and in many specimens it is not observed at alL Stolonal tubes. The width of stolonal tubes, minus the marginal membrane, amounts to 130 to 158 !-t, averaging 154 !-t, and the width of their fuselli fluctuates within limits of 30 and 58, averaging 39 !-t. The lower, flat wall of stolonal tubes is frequently lacking. It is much thinner than the convex wall. Stolons. In transverse section, stolons are semicircular, with an upper wall convex and lower flat and several times thinner than the convex one. The width of stolons varies from 25 to 51 !-t, averaging 38 !-t. Such a variability is even observed within a specimen of a bifurcated stolon. In places of bifurcation, a lateral stolon may be separated from the main B D E Fig. 2 RHABDOPLEURA KOZLOWSKII FROM THE BATHONIAN 419 one by a few diaphragms having 7-9 f..L wide pores. The diaphragms are mostly situated in contractions of the vesicular extensions of the proximal part of the lateral stolon. Peduncular and lateral stolons detach them­ selves alternately from the main one at intervals of about 310 to 630 f..L. Peduncular stolons are short and vesicular, mostly provided with two or three diaphragms having 4-9 f..L wide (averaging 7 f..L) pores. Peduncular stolons with a higher number of diaphragms were also observed (Fig. 5 B, C3). c 2. A B Fig. 3. - Rhabdopleura kozlowskii Kuticki (Z. Pal. Pb. II/8-10): A a zooidal tube, Bathonian, Blanowice; B-C zooidal tubes, Callovian, Luk6w: 1 a fusellar layer of a zooidal tube, 2a, 2b particular laminae of a secondary layer. Cysts of dormant buds. The cysts of dormant buds resemble in shape the proximal part of a contractile stalk of a zooids (Schepotieff, 1907) and they are formed on its basis (Stebbing, 1970). The width of the cysts of dormant buds, which closely adhere to the waUs of stolonal tubes, varies ---- ~~--- -------- Fig. 2. - A Rhabdopleura sp., Bathonian, Blanowice: zooidal tubes connected by common fuselli (Z. Pal. Pb. II/I); B-F Rh. kozlowskii Kulicki, Bathonian, Blanowice: erect part of zooidal tubes (Z. Pal. Pb. II/2-7); G-H Rh. normani Allman, Recent, Bergen, Norway: bifurcated zooidal tubes (Z. Pal. Pb. 1/101). A E F Fig. 4 RHABDOPLEURA KOZLOWSKII FROM THE BATHONIAN 421 within limits of 85 and 166 11, averaging 129f!, and their length 260 and 460 !!, averaging 344 !!. Remarks. - The dimensions of the specimens of Rh. kozlowskii from the Bathonian of Blanowice are contained within the range of individual variability of the specimens of this same species from the Callovian of Luk6w. Mean dimensions of the elements of tubarium are approaching each other in the two forms. In other respects, the stolonal tubes and cysts of dormant buds in the Bathonian form do not differ radically from the Callovian one or from the remaining species, except for Rh. striata. A certain number of peduncular stolons, divided by a larger number of diaphragms and being longer than those of the Callovian, specimens from Luk6w (Fig. 5, B, C3), which occur among the Bathonian specimens make up a small differences between them. This difference is, however, too small to constitute a basis for the distinction of the Bathonian form as a separate species. As follows from Kozlowski's (1956) and Kulicki's (1969) studies, the structure of peduncular stolons and the shape of the transverse section of the main stolon are of a decisive importance to distinguishing species. The secondary layer, internally lining the ascending parts of zooidal tubes, is a quite new skeletal element observed in Rh. kozlowskii only. The occurrence of a thicker or bilaminate secondary layer inside the tubes with small or normal diameters or its frequent lack in the tubes with large diameters, indu-ce the present writer to conclude that the secondary layer played a reinforcing role. Its presence and degree of thickening depend on the length and diameter of the tubes and on envi'ronmental conditions. What is known as longitudinal ribs, occurring inside woidal tubes between the creeping and ascending part of a tube was described by Schepotieff '(1907) in Rh. normani as reinforcing elements. This author found that, in the case of short zooidal tubes, the longitudinal ribs do not occur at all or are poorly developed. No ·reinforcing elements have been found in Rh. vistulae Kozlowski. Figs. 2 Al and A z show zooidal tubes, which closely adhere to each other and whose fusellar systems are connected with each other by common fuselli.
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